Internal combustion engines include a cylinder head and cylinder block connected to form cylinders. The engine may include intake valves positioned in intake ports. The intake valves may be used to provide the cylinder with air. The engine may further include exhaust valves positioned in exhaust ports. The exhaust valves are used to flow combustion gasses away from the cylinders.
A higher degree of throttling may be used when the engine has a low load. When throttling is increased engine efficiency is decreased and specifically charge exchange losses are increased. In order to increase engine efficiency and reduce the throttling losses, different strategies for load control have been developed.
For example, variable valve timing may be used in engines to enable the timing of the intake and/or exhaust valves to be advanced or retarded. Variable valve timing may enable an increase in engine efficiency. Attempts have been made to vary the valve timing using a camshaft adjusting device with which the camshaft can be rotated through a given angle with respect to the crankshaft, so that the control times can be advanced or retarded, without the ability to independently vary the opening and closing durations of the valves. Therefore, crankshaft adjustment devices displace the opening time and the closing time by the same crank angle amount in the same direction. The intake and/or exhaust valves may be advanced or retarded such that valve overlap occurs across different cylinders. That is to say, the intake valve in one cylinder is open while the exhaust valve in another cylinder is also open. Valve overlap may lead to cylinder cross-talk. As a result, engine efficiency may be decreased. Cylinder cross-talk may be exacerbated in cylinder heads having exhaust manifold integrated therein and/or shortened exhaust manifold used to reduce losses in turbocharged systems.
The Inventors herein have recognized at least some of the above issues and developed a method for controlling valve actuation in an engine is provided. The method includes initiating combustion operation in a first cylinder, opening, via a first cam, a first exhaust valve coupled to the first cylinder for a first opening duration. The method further includes opening, via a second cam, a second exhaust valve coupled to the first cylinder for a second opening duration not equivalent to the first opening duration.
The variation in the opening durations reduces cross-talk between combusted cylinders. In one example, the first opening duration is longer than the second opening duration and the first exhaust valve is closer to a precedingly combusted cylinder than the second exhaust valve, the precedingly combusted cylinder directly preceding the combustion in the first cylinder in the firing order. In this way, the opening duration of an exhaust valve closer to a previously combusted cylinder is shortened to reduce the likelihood of cross-talk between the cylinders. As a result, combustion efficiency is improved, thereby improving the engine's efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.
The internal combustion engine is described in greater detail below with reference to the illustrative examples shown in FIGS. 1-2.